1. Field of the Invention
The present invention is directed to implants, and in particular to glaucoma implants including biocompatible porous regions, which form a hollow reservoir with a base region so that excess aqueous humor may flow from the anterior chamber of an eye into the hollow reservoir. The invention is also directed to making and surgically implanting such implants.
2. Discussion of the Background
Glaucoma is a disease whereby the intraocular pressure (IOP) is too high for the health and viability of an optic nerve of an eye. If untreated, the high intraocular pressure eventually damages the optic nerve, and may lead to blindness.
Glaucoma can be controlled in many patients by lowering the IOP. This may be accomplished by using topical medications, laser treatment or trabeculectomy to increase an outflow of aqueous humor from the anterior chamber of the eye. When these methods fail to control intraocular pressure, ophthalmic surgeons may use setons, or aqueous drainage devices (glaucoma shunts) to remove aqueous humor from the anterior chamber, and thus reduce high levels of intraocular pressure. Currently, these devices are used as a secondary intervention because of their relatively high complication and failure rates.
Conventional glaucoma shunts, such as those disclosed in U.S. Pat. Nos. 5,338,291 and 5,476,445, both of which are incorporated by reference, include a catheter (i.e., a drainage tube) attached to a base plate. A free end of the catheter is surgically implanted into the anterior chamber of the eye. The base plate is sutured to an outside of the globe beneath the conjunctiva. The glaucoma implant functions as a drain over the first three to six postoperative weeks as the silicone plate is enclosed by a fibrous capsule. The fibrous capsule allows a space to form into which fluid can drain and from which fluid can be absorbed by the surrounding tissues. Ideally, the size and thickness of the fibrous capsule (i.e., the filtering bleb) that surrounds the base plate is such that the amount of fluid that passes through the capsule is identical to the amount of fluid produced by the eye at an intraocular pressure of 8 to 14 mmHg. Thus, aqueous humor can be drained from the anterior region of the eye, through the drainage tube to the filtering bleb, where the fluid can be absorbed by the surrounding tissue.
Conventional glaucoma shunts, such as the Molteno, Shocket, and Baervaldt glaucoma shunts, are made of silicone or polypropylene, a material approved for human implant use, but which exhibits biocompatibility difficulties when the material is implanted on the sclera underneath the conjunctiva of the eye. Thus, long term performance of these shunts is inadequate.
The primary cause of failure is a foreign body tissue response to the silicone or polypropylene material, which results in encapsulation of the drainage reservoir formed by the base plate of the shunt. Thus, the absorption of the drained aqueous humor is prevented, and an increased back pressure of the anterior chamber occurs. That is, in conventional glaucoma shunts, the healing response includes chronic inflammation and fibrosis of the shunt, which results in a decreased outflow of the aqueous fluid of the conjunctival space caused by the development of the fibrous capsule around the shunt.
One of the major approaches to solving the above-noted problems involves surface modification of the base polymer. For example, U.S. Pat. No. 5,338,291, discloses a method of texturing the surface of the base plate to interrupt the formation of a dense fibrous capsule and to promote vascularization around the base plate. Although these approaches have increased the life-time of the glaucoma shunt, the long-term function of the conventional glaucoma shunt is still inadequate.
Accordingly, one object of the invention is to provide a novel glaucoma shunt and a method of making and surgically implanting the same, which results in an improved healing response from surrounding tissues.
Another object of the invention is to provide a novel glaucoma shunt, which results in a dramatic reduction in the formation of a dense, fibrous capsule around the shunt.
Still another object of the invention is to provide a novel glaucoma shunt, which includes porous regions, so that new blood vessel growth occurs into pores, channels, or interstices of the porous material.
Yet another object of the invention is to provide a novel glaucoma shunt which has a long-term life expectancy.
These and other objects may be accomplished by providing a novel glaucoma shunt, including a first porous region, a second porous region connected to the first porous region, and a third region having edge areas attached to edge areas of the second region so as to form a hollow reservoir therebetween. Also provided is a catheter having an end between the second and third regions. In addition, the first and second regions may include, for example, expanded polytetrafluoroethylene (ePTFE), polyurethane, and elastomeric silicone, which have pores with diameters within a range of 1 xcexcm to 500 xcexcm. The second region may include, for example, expanded polytetrafluoroethylene (ePTFE), polyurethane, and elastomeric silicone, which have pores with diameters less than or equal to 0.8 xcexcm. In addition, the connected first and second regions may have a permeability defined as a water flow through rate of at least 1.0 microliter/minxc2x7cm2 at a water entry pressure of 100 mmHg.
Also provided is a method making the above novel glaucoma shunt. The method includes connecting (e.g., laminating or bonding) first and second porous regions 11 and 12, and then attaching (e.g., fusing or sealing) edge areas of a third region 13 to edge areas of the second region 11 so as to form a hollow reservoir therebetween. In addition, a catheter 7 having a first end is sandwiched between the second region 12 and third region 13.
In addition, a method of treating glaucoma using the above-noted novel glaucoma shunt is provided. This method includes surgically inserting one end of the catheter into the anterior chamber of the eye, and surgically implanting the base plate having the connected first and second porous regions attached to the third region beneath the conjunctiva of the eye.